Core A is an essential component of this Program Project, as it serves the research needs of four of the five Projects proposed by the Principal and Co-Investigators. The major research instrument in the Core is a JEOL 100 CX II electron microscope, originally purchased by funds primarily provided by this Program Project in 1986. The electron microscope permits analysis of neurons and their synaptic connections. Many of the studies proposed in this application deal with changes in neural networks that are believed to underlie pain syndromes, and the work could not be carried out without the instrument. The funds requested in the Core A budget support part of the salary of a senior electron microscopy technician, who oversees the unit, trains new users of the microscope, and keeps it in optimal running order. Funds are also requested to pay 50% of the annual cost of a service contract. An additional instrument, a BioRad Scanning Confocal microscope, is housed in the Keck Foundation Center for Integrative Neuroscience; three of the Co-Investigators are members of the Center. The confocal microscope is used to examine populations of neurons stained by immunofluorescence to identify various synaptic transmitters and receptors. Several of the research projects in this proposal make use of this instrument as a research tool. Fifty percent of the annual cost of a service contract of the confocal microscope is requested in this proposal.